It is common practice to provide means for applying a retarding force to a shaft or other rotating part of a machine, to compensate for looseness caused by wear. Such slack in the power transmission system tends to create "chatter", and to produce inaccuracy when machining operatives are involved. In some instances, for example, as much as two degrees of backlash can result from gear train wear when the working load upon tooling is relieved, and the attendant problems may be particularly acute in those instances in which small tools, which must be handled with considerable delicacy, are involved. Although many different forms of machines suffer from difficulties of this nature, those in which constant and frequent indexing occurs, such as in automatic screw machines, represent specific instances in which it is particularly important to damp spurious movement caused by wear.
As indicated, this has been accomplished in the past by creating a drag upon a shaft of the machine, developed by frictional force that is applied either continuously or intermittently. The former approach is disadvantageous for a number of reasons, including the need that it creates for overpowering of the machine, so as to ensure the availability of sufficient net energy for providing the desired speed and other characteristics of operation; also, there is of course a substantial waste of energy and the generation of excessive amounts of heat.
Other forms of devices apply the retarding force only during the working phase of the cycle, relieving it when indexing is to occur. While offering obvious advantages over constant-drag arrangements, the prior art systems of this type have typically relied upon springs or hydraulic and pneumatic means to effect the dynamic action required; furthermore, they have not been entirely satisfactory in operation, and they have tended to be overly complex and prone to premature failure.
Accordingly, it is the broad object of the present invention to provide a novel automatic brake assembly for intermittently applying braking force to a rotating member, and for relieving such force therefrom.
A more specific object of the invention is to provide such an assembly which is purely mechanical in nature, is highly effective, safe and reliable, and which is of uncomplicated construction, thereby rendering it relatively inexpensive and facile to manufacture.
Another specific object is to provide a device having the foregoing features and advantages, in which the application and the relief of retarding force to the rotating machine component are both effected in a positive manner, and which enhances performance and efficiency of the machine.
A further specific object of the invention is to provide such a device which is constructed to enable facile installation and to avoid interference with other cam-operated attachments, and particularly with attachments on an automatic screw machine.
Yet another object is to provide a novel brake band member which is particularly well-suited for use in such a brake assembly, and which further enhances efficiency and longevity of the mechanism.